Incubation of Chinese hamster cells at an elevated but sublethal temperature between fractions of radiation and/or pulses of hyperthermia at 45.degree. C strongly modified the effectiveness of cell killing. Increasing the incubation temperature from 37 to 40.degree. C between fractions of hyperthermia at 45.degree. C followed by radiation substantially enhanced cell killing while the opposite sequence (radiation .fwdarw. incubation at 40.degree. C .fwdarw. hyperthermia at 45.degree. C) resulted in less effective cell killing than would have been expected from the independent interaction of hyperthermia and radiation alone. This suggests the use of short pulses of localized hyperthermia in the presence of physiologically tolerable fever followed by irradiation as 1 approach to the utilization of hyperthermia in cancer therapy.